In the medical field, research is being actively pursued on optical imaging devices that irradiate a living body with light from a light source, such as a laser, and visualize information about the inside of the living body acquired based on the light that has entered. Photoacoustic imaging is one of these optical imaging technologies. In photoacoustic imaging, a living body is irradiated with pulsed light generated from a light source. Acoustic waves (typically ultrasonic waves) generated from biological tissues that have absorbed the energy of the pulsed light having propagated and diffused inside the living body are detected. Based on the detected signal, information about the inside of the living body is visualized. Specifically, by utilizing a difference in the light-energy absorption rate between a target part, such as a tumor, and the other tissues, an acoustic wave detector detects elastic waves generated when the target part instantaneously expands in response to absorption of the energy of the irradiated light. By mathematically and analytically processing this detected signal, a distribution of optical properties inside the living body or information related to the distribution of optical properties, particularly, a distribution of initial sound pressures, a distribution of optical energy absorption densities, and a distribution of optical absorption coefficients, and so forth, can be acquired.
In photoacoustic imaging, it is necessary to stably maintain the shape of a subject during measurement in order to acquire appropriate images. Thus, PTL 1 illustrated in FIG. 10 discloses a technique for stably maintaining the shape of a subject to acquire information about the subject. Specifically, PTL 1 discloses a technique for stably maintaining the shape of a subject by holding the subject between two press plates 2a and 2b, and for receiving acoustic waves by performing scanning with one acoustic wave receiver 5. In addition, in PTL 1, the press plate 2b is used as a scanning surface of the acoustic wave receiver 5.